CN1747972A - Aqueous polymer dispersion and process - Google Patents

Abstract

The present invention relates to a method for preparing an aqueous polymer dispersion by microemulsion polymerization, the method comprising the steps of: (a) forming At least one amphiphilic stabilizing polymer with an acid value of g (optionally both formed into a first aqueous premix) and at least one hydrophobic co-stabilizer and at least one α,β-olefin a mixture of unsaturated monomers (optionally both formed into a second organic premixture); (b) subjecting this mixture to high stress to form a microemulsion comprising stable droplets having an average diameter of about 10 to about 1000 nm, and Monomers that polymerize inside the droplet. Preferably the mixture is substantially free of surfactants other than the amphiphilic polymer. The obtained aqueous polymer dispersions and their use in coatings, films, adhesives and inks are also described.

Description

Aqueous polymer dispersions and methods for their preparation

The invention relates to a method for preparing an aqueous polymer dispersion by microemulsion polymerization, the prepared polymer dispersion and its application.

Aqueous polymer dispersions have been prepared by microemulsion polymerization for several years. In the preparation method, the monomer is dispersed with nano-scale liquid droplets, constituting the dispersed phase of the oil-in-water emulsion. Monomer emulsions for microemulsion polymerization have average droplet diameters from 10 to 1000 nm and can be distinguished from conventional monomer emulsions and emulsion polymerization processes in which the size of the droplets or micelles is greater than 1-10 μm (micrometer). In the microemulsion approach, each nanoscale droplet becomes the primary site for nucleation and consequent polymerization in a highly parallel fashion, producing polymer latex particles approximately the same size as the initial droplet. Compared with ordinary emulsion polymerization, microemulsion polymerization has several advantages, for example, hydrophobic components are encapsulated or incorporated into the polymer during polymerization.

Common emulsion polymerization uses monomers, water and surfactants as ingredients. Microemulsion polymerization requires the addition of other components to stabilize the small emulsion droplets formed before and during polymerization. These additional components are generally hydrophobic components with no water solubility or very low water solubility and good miscibility with the monomer.

WO 00/29451 and US 5,686,518 disclose a series of hydrophobic components suitable for microemulsion stabilization. These documents teach that, in addition to these hydrophobic components, surfactants are required to stabilize both the emulsion droplets and the resulting polymer particles after polymerization. The surfactants used are: sodium lauryl sulfate or other alkyl sulfates, sodium dodecylbenzenesulfonate or other alkyl or arylsulfonates, sodium stearate or other fatty acid salts, or poly vinyl alcohol.

US 2002/131941 A1 (BASF) (=EP 1191041) describes pigmented aqueous polymer dispersions for use as cosmetics, the average particle size of which is below 1000 nm. Organic UV absorbers and colorants are a major part of these emulsions and their presence significantly affects the stability and particle size distribution of the droplets within the emulsion and the properties of the resulting final polymer dispersion. These cosmetic compositions therefore behave very differently from colorant-free dispersions. This reference addresses the issue that anionic emulsifiers used in the past to stabilize prior art compositions cause skin irritation and teaches the use of an alternative stabilizing system comprising at least 0.1-20% of at least one non-ionic surface Active compound (NS) with 1-50% of at least one amphiphilic polymer (PA) having 0.5 to 10 mol/kg anionic functional groups, these percentages being based on the weight of the polymer matrix. Amphiphilic polymers are not used as the sole surfactant in this system, since a nonionic surfactant must be added to stabilize the dispersion. The use of hydrophobic co-stabilizers (non-surface active) of the type described here is not mentioned in this document. Skin compatible organic amines such as aminoalcohols are preferably used to neutralize the anionic groups of these amphiphilic polymers. Other differences between US 2002/131941 and the present invention are as follows: The amphiphilic polymers described are limited to those obtained by addition polymerization. The resulting polymer composition has a low solids content (<21%) and has a high Tg. The dispersions exemplified in the reference contained relatively large (approximately 5%) amounts of coacervate polymer. During the polymerization of these dispersions, a water-soluble free-radical generating compound is added to the reactor, ie usually dispersed or dissolved in the continuous (aqueous) phase. In contrast, in the process of the present invention, the free radical generator can be introduced directly into the organic phase prior to dispersion.

US 5,952,398 (3M) describes pressure sensitive adhesives (PSAs) prepared by microemulsion polymerization. The PSA has two bicontinuous phases, a hydrophobic PSA polymer and a hydrophilic polymer. These compositions are prepared from surfactant stabilized oil-in-water microemulsions. The aqueous continuous phase comprises free radically polymerizable ethylenically unsaturated polar amphiphilic or hydrophilic monomers or oligomers. The dispersed oil phase comprises micron-sized droplets of free-radically polymerizable ethylenically unsaturated hydrophobic monomers, which upon polymerization form large micron-sized polymer particles. When the aqueous polymer dispersions of this document are used to form coatings or films, the presence of large amounts of surfactants tends to lead to defects such as facilitating migration or aggregation of ingredients into hydrophilic pockets. Surfactants also adversely affect the desired properties of such coatings or films, for example by increasing water sensitivity or causing other problems such as water whitening and weathering.

The present invention overcomes some or all of the problems of the prior art by providing a process for the preparation of aqueous dispersions by microemulsion polymerization in which undesired surfactants can be eliminated or their levels can be significantly reduced.

So broadly according to the present invention there is provided a process for the preparation of aqueous polymer dispersions by microemulsion polymerization comprising the steps of

(a) forming a mixture comprising:

(i) water;

(ii) at least one amphiphilic stabilizing polymer having a number average molecular weight (Mn) of about 800 to about 100,000 Daltons and an acid value of about 50 to about 400 mg KOH/g;

(iii) at least one hydrophobic co-stabilizer; and

(iv) at least one α,β-ethylenically unsaturated monomer;

wherein the mixture comprises no more than about 2% by weight, relative to the total amount of any other ingredients, of a monomer that acts as a surfactant in the mixture;

(b) applying high stress to the mixture of step (a) to form a substantially stable microemulsion comprising a continuous aqueous phase and dispersed therein stable droplets having an average diameter of about 10 to about 1000 nm, the liquid Droplets contain hydrophobic co-stabilizers and monomers

(c) monomers polymerized inside the droplet;

Optionally, the method of the invention is subject to at least one of the following conditions:

(w) the mixture in step (a) comprises less than 0.1% of the total amount of any nonionic surface active compound;

(x) Hydrophobic co-stabilizers do not also act as surfactants (ie, they are substantially absent from the interface between the dispersed organic phase and the continuous aqueous phase)

(y) the hydrophobic co-stabilizer is substantially colorless; and/or

(z) Any acid groups on the amphiphilic stabilizing polymer are neutralized with at least one strong base, optionally selected from alkali metal hydroxides and ammonia.

It will be appreciated that the polymerization reactions described herein can be carried out in batch, continuous and/or semi-continuous processes. If desired, it is possible to add additional monomer to the continuous phase to diffuse into the dispersed droplets. For example, if it is desired to control the relative concentration of the monomers in the dispersed droplets (e.g., to prevent significant changes in the composition of the resulting polymer as the polymerization proceeds), an appropriate amount of one or more monomers can be added during the polymerization. Add to the mixture at an appropriate time.

It has been found that the amphiphilic stabilizing polymers defined herein allow the preparation of stable microemulsions without the addition of large amounts, preferably any, of common surfactants such as alkyl, aryl, alkylaryl and aryl Alkyl sulfates and sulfonates.

The amphiphilic stabilizing polymer used in the method of the invention exhibits a suitable balance of hydrophobicity and hydrophilicity, which makes it suitable for the stabilization of oil-in-water emulsions. Preferred amphiphilic stabilizing polymers include polymers obtained from combinations of hydrophobic monomers and hydrophilic monomers, which polymers incorporate acid functional groups or those functional groups capable of forming acid functional groups.

Preferably the mixture formed in step (a) contains less than about 1%, more preferably less than about 0.5%, most preferably less than 0.1% of additional surfactant. Conveniently, the mixture of step (a) is substantially free of additional surfactant. Advantageously, the only component in the mixture of step (a) usable as surfactant in the microemulsion formed in step (b) is the amphiphilic stabilizing polymer.

Hydrophobic co-stabilizers are not used here as normal nonionic surfactants because they are soluble in hydrophobic monomers but very insoluble in water. The hydrophobic co-stabilizer is present mainly, preferably substantially only, in the hydrophobic phase and not at the interface between the hydrophobic and hydrophilic phases, the latter being used as a common nonionic surfactant. material condition. Hydrophobic co-stabilizers are used to stabilize the dispersed monomer. In the preferred process of the present invention, it is not necessary to use additional surfactants, such as additional nonionic surfactants, to prepare stable dispersions.

The amphiphilic stabilizing polymer is more preferably derived from one or more ethylenically unsaturated hydrophobic monomers, such as styrene, (meth)acrylates, isobutylene and their derivatives, with one or more An ethylenically unsaturated hydrophilic monomer, such as carboxyl-containing monomers (such as acrylic acid, methacrylic acid, itaconic acid), sulfonic acid monomers or their salts (such as styrenesulfonic acid and 2-acryloyl amino-2-methyl-propanesulfonic acid), phosphate monomers (e.g. ethylene glycol methacrylate phosphate), phosphonate monomers (e.g. vinylphosphonic acid), acid anhydrides (e.g. maleic anhydride), The latter are selectively hydrolyzed or modified by alcohols or amines, obtained by addition polymerization of copolymers.

Conveniently, the amphiphilic polymer is substantially unpigmented, so the resulting dispersion is also colorless.

Other amphiphilic polymers suitable for use in the process of the invention are those obtained by stepwise polymerization, such as polyurethanes and polyesters containing pendant acid functional groups. Suitable polyurethane polymers are those obtained from polyurethane prepolymers which are the reaction product of:

(i) at least one polyisocyanate (such as isophorone diisocyanate, dicyclohexylmethane diisocyanate and/or tetramethylxylylene diisocyanate),

(ii) at least one organic compound comprising at least two reactive groups capable of reacting with isocyanates (such as polyester polyols, polyether polyols and/or polycarbonate polyols having from about 400 to about 5,000 the preferred number average molecular weight (Mn) of Tn), and

(iii) At least one alcohol or polyol capable of reacting with isocyanate groups and containing additional functional groups that provide good dispersibility in water and that can provide acid functionality. The alcohol or polyol may have functional groups such as anionic salt groups or similar precursors which can subsequently be converted into anionic salt groups such as carboxylate or sulfonate groups. The carboxylate groups to be introduced into the isocyanate-terminated polyurethane prepolymer used in the process of the present invention can be obtained from hydroxycarboxylic acids, such as those represented by the following formula 1

(HO) _x R(COOH) _y general formula 1, where

R represents a linear or branched hydrocarbon residue having 1 to 12 carbon atoms, and x and y are independently an integer of 1 to 3.

More preferred hydroxycarboxylic acids are α,α-dimethylolalkanoic acids, (ie x=2 and y=1 in Formula 1), such as 2,2-dimethylolpropionic acid.

More preferred amphiphilic polymers include copolymers obtained from styrene and maleic anhydride and/or copolymers obtained from styrene, alpha-methylstyrene and acrylic acid.

Conveniently, the amphiphilic polymer used in the method of the present invention has a solubility in the aqueous phase of the microemulsion (measured at 25° C.) of at least about 1×10 ⁻² g/l, more conveniently at least about 1×10 ^{- 1} g/l, and most suitably at least about 1 g/l.

Preferred amphiphilic polymers have a Mn of from about 900 to about 50,000 Daltons, more preferably from about 1,000 to about 25,000.

Preferred amphiphilic polymers have an acid number of from about 100 to about 350 mg KOH/g, more preferably from about 150 to about 300 mg KOH/g. Acid number as used herein is defined as the amount of potassium hydroxide (expressed in milligrams) required to completely neutralize 1 gram of polymer.

The amount of amphiphilic polymer used in the process of the present invention can generally be from about 0.5% to about 15% (by weight) of the monomers (relative to the total amount of α,β-ethylenically unsaturated monomers used). The amount is expressed as the total weight percent of the amphiphilic stabilizing polymer). The amount of amphiphilic stabilizing polymer is preferably from about 1% to about 8%, more preferably from about 2% to about 5%, by weight, of the monomers.

The hydrophobic co-stabilizers used in the process of the invention are highly water insoluble but highly soluble in α,β-ethylenically unsaturated monomers. Conveniently, the hydrophobic co-stabilizer has a solubility in water (measured at 25°C) of less than about 5 x 10 ^-5 g/l, more suitably less than about 5 x 10 ^-6 g/l.

Preferred hydrophobic co-stabilizers comprise one or more of the following components:

Hydrocarbons, more preferably alkanes or cycloalkanes, most preferably having at least 12 carbon atoms (such as hexadecane and/or octadecane);

long-chain alcohols (such as cetyl alcohol and/or stearyl alcohol);

halogenated hydrocarbons,

organosilicon compound,

long chain esters,

Oils, more preferably vegetable oils (such as olive oil),

hydrophobic dye molecules,

blocked isocyanate,

oligomers and/or polymeric products of polymerization, polycondensation or polyaddition, such as polymeric co-stabilizers (such as those described in US 5,686,518, the contents of which are hereby incorporated by reference); and/or suitable mixtures thereof and / or conjugates.

Conveniently, the hydrophobic co-stabilizer is not strongly colored unless it does not react during the polymerization reaction in another aspect of the process as described below.

In yet another aspect of the method of the present invention, the hydrophobic co-stabilizer is reactive and can be used with or without an additional non-reactive hydrophobic co-stabilizer. Reactive hydrophobic co-stabilizers mean those co-stabilizers which take part in subsequent polymerization reactions.

Preferred reactive hydrophobic co-stabilizers include one or more of the following components:

Hydrophobic (co)monomers, more preferably acrylates, most preferably stearyl acrylate and/or long chain (meth)acrylates,

large monomer

Hydrophobic chain transfer agents, more preferably dodecyl mercaptan, stearyl mercaptan and/or other long chain mercaptans;

Hydrophobic initiators, more preferably 2,5-dimethyl-2-5-bis(2-ethylhexanoylperoxy)hexane and other long-chain (hydro)peroxides, and/or azo-initiated agents and/or suitable mixtures and/or combinations thereof.

Typically hydrophobic co-stabilizers are selected from C _12-24 alkanes (especially hexadecane), C _12-24 alcohols, C _18-22 acrylates (especially acrylates commercially available as Norsocryl ^™ A-18-22 from Atofina mixtures); and/or mixtures thereof.

If the hydrophobic (co)monomer is used as both a hydrophobic co-stabilizer and an α,β-ethylenically unsaturated monomer, the amount of the hydrophobic (co)monomer can be as high as about 70% by weight. Typically, hydrophobic co-stabilizers can be added in an amount of from about 0.05% to about 40% by weight. Especially when the hydrophobic co-stabilizer is not a (co)monomer, the co-stabilizer is preferably present in an amount from about 0.1% to about 10%, more preferably from about 0.2% to about 8% and most preferably from about 0.5% to About 5% by weight. The weight of hydrophobic co-stabilizers used here is calculated relative to the total weight of the mixture prepared in step (a) of the process according to the invention.

The α,β-ethylenically unsaturated monomers typically used in the process of the present invention have low solubility in water, preferably (measured at 25° C., as a percentage of grams of dissolved monomer per 100 grams of water) of less than about 15%, More preferably less than about 5%, and most preferably less than about 3%.

Preferred α,β-ethylenically unsaturated monomers include one or more of the following monomers and/or mixtures and/or combinations thereof:

Alkyl (meth)acrylates, more preferably methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, Cyclohexyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, isobornyl methacrylate and/or lauryl methacrylate, most preferably methyl methacrylate, Methyl acrylate, n-butyl acrylate, ethyl acrylate and/or 2-ethylhexyl acrylate,

polymerizable aromatic compounds; more preferably styrene, most preferably styrene, alpha-methylstyrene, vinyltoluene and/or tert-butylstyrene,

polymerizable nitriles; more preferably acrylonitrile and/or methacrylonitrile,

polymerizable amides,

α-olefin compounds such as ethylene,

Vinyl compounds; more preferably vinyl esters (most preferably vinyl acetate, vinyl propionate and/or longer chain vinyl ester homologues), vinyl ethers, vinyl halides (most preferably vinyl chloride) and/or or vinylidene halide,

Diene compounds, more preferably butadiene and/or isoprene,

α,β-Ethylenically unsaturated monomers containing fluorine and/or silicon atoms, more preferably 1H,1H,5H-octafluoropentylacrylate and/or trimethylsiloxyethylacrylate.

Advantageously, the α,β-ethylenically unsaturated monomers are selected from the group consisting of styrenes, acrylates, methacrylates, vinyl and vinylidene halides, dienes, vinyl esters and mixtures thereof more advantageously selected from methyl methacrylate, styrene, vinyl acetate, methyl acrylate, butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, butadiene and vinyl chloride.

The α,β-ethylenically unsaturated monomer used in the method of the present invention can generally be used in an amount of about 10% to about 70%, preferably about 18% to about 60% by weight, relative to the steps of the method of the invention ( Calculate the total weight of the mixture prepared in a).

According to yet another aspect of the method of the present invention, one or more water-soluble monomers (represented herein as secondary monomers) may be added to step ( In the mixture formed in a). These optional secondary monomers may include ethylenically unsaturated organic compounds capable of addition polymerization. Preferred secondary monomers have a water solubility (measured at 25°C as the percentage of grams of dissolved monomer per 100 grams of water) greater than about 15%. Conveniently, secondary monomers may be used only in the presence of at least one α,β-ethylenically unsaturated monomer and only in a minor percentage in the monomer mixture. The preferred amount of optional secondary monomers in the above monomer mixture (relative to the total monomer weight) is less than about 6%, more preferably from about 0.1% to about 4%, and most preferably from about 0.1% to about 2% (by weight).

Preferred secondary monomers are acrylic acid, methacrylic acid, 2-sulfoethyl methacrylate, and/or maleic anhydride. The secondary monomers used in the process of the invention are capable of imparting the desired properties to the coating produced from the resulting polymer dispersion.

The mixture formed in step (a) may also contain one or more components to adjust the pH. For example, if the stabilizing amphiphilic polymer contains carboxylic acid groups, it may be necessary to prepare and polymerize the microemulsion at high pH so that the stabilizing polymer exhibits the desired amphiphilic properties. For carboxylic acid functional polymers, a suitable pH range may be from about 6.0 to about 10.0, preferably from about 7.5 to about 10.0, depending on the nature of the other components of the amphiphilic polymer. When the stabilizing polymer comprises acid functional groups formed from sulfonic acid, sulfate, phosphate or phosphonate, a suitable pH range may be from about 2.0 to about 10.0.

Compounds that can adjust pH include: ammonia, amines (e.g. triethylamine, triethanolamine, dimethylaminohydroxypropane), carbonates (e.g. sodium carbonate), bicarbonates (e.g. sodium bicarbonate), hydrogen Oxides such as sodium hydroxide and/or oxides such as calcium oxide. Preferred pH adjusting compounds are strong bases, optionally selected from alkali metal hydroxides (such as sodium hydroxide) and/or ammonia.

The pH adjusting compound may be added during step (a) of the process of the invention, preferably before the amphiphilic polymer is added to the mixture.

Each step of the method of the invention can be carried out independently under any suitable conditions selected according to the reagents used. Conveniently, any of the steps may be carried out at any suitable temperature between the freezing and boiling points of the various mixtures and components present therein, more conveniently from about 0°C to about 100°C, most conveniently at about room temperature. Conveniently, these steps may be performed at a pressure of from about 0.01 to about 100 atmospheres, more conveniently at about atmospheric pressure.

In yet another aspect of the method of the present invention, in step (a), the mixture may conveniently be prepared by mixing a first premix comprising an amphiphilic stabilizing polymer and water with a co-stabilizer comprising hydrophobicity and α,β - a second premixture of ethylenically unsaturated monomers is formed.

The first premix can be prepared by adding an amphiphilic stabilizing polymer to water, preferably at a temperature of from about 0°C to about 100°C, followed by the addition of one or more optional ingredients (described herein and identified as Amounts described here): eg surfactants, secondary water-soluble monomers; pH adjusting compounds and/or polymerization initiators.

If the first premix is prepared using an amphiphilic stabilizing polymer comprising carboxylic acid functional groups, a pH adjusting compound may be added to adjust the solubility of the amphiphilic polymer in the first premix (i) ( measured at 25°C) to at least about 1 x 10 ^-2 g/l, more preferably at least about 1 x 10 ^-1 g/l, most preferably at least about 1 g/l. The pH adjusting compound is preferably added to the amphiphilic polymer before the polymer is added to the water and any optional additional components of the first premix.

A second premix can be prepared by adding the desired amount of hydrophobic co-stabilizer to the α,β-ethylenically unsaturated monomer, preferably with gentle agitation. It is also preferred to prepare the second premix at room temperature, more preferably until a clear solution is obtained. Optionally, one or more secondary water soluble monomers (described herein) and/or polymerization initiators may also be added to the second premix.

In step (a), the formation of the mixture is preferably accomplished at a temperature of from about 0°C to about 100°C, preferably at about room temperature.

Preferably in step (b) of the process of the invention, the mixture of step (a) is mixed until a microemulsion comprising stabilized droplets is formed, said droplets having a diameter of from about 10 to about 900 nm, more preferably from about 50 to An average particle size of about 500 nm, more preferably from about 80 to about 450 nm, such as from about 100 to about 430 nm.

The droplet size is measured here by diluting a sample of the microemulsion with deionized water (or preferably diluted with deionized water saturated with the monomers present in the microemulsion). The average droplet size of the samples is determined directly within 15 minutes by using dynamic light scattering, for example, on a Coulter ^™ N4 Plus or Nicomp 380 ZLS device.

In step (b), the mixture is mixed under high stress. Stress is described as force per unit area. One way of applying stress is shear. Shear means that a force causes a single layer or plane to move parallel to an adjacent single layer or plane. Stresses can also be applied from all sides as volumetric stresses, compressive stresses, so that there is hardly any shear when the stresses are applied. Another way of applying stress is through cavitation, which occurs when the pressure within a liquid drops sufficiently to cause vaporization. Bubbles form and collapse violently in a short time and generate intense stress. Another way to apply stress is to use ultrasonic energy. Preference is given to using equipment capable of localized high shear, preferably also moderate bulk mixing. High shear mixing is more preferably achieved using sonication, colloid mills and/or homogenizers.

Monomer microemulsions can be usefully formed at any temperature between the freezing and boiling points of the mixture and the components present therein, preferably from about 20 to about 50°C, more preferably from about 25 to about 40°C, most preferably at about at room temperature.

Step (b) of the process of the present invention produces a substantially stable microemulsion comprising a continuous aqueous phase and a dispersed phase of droplets comprising an α,β-ethylenically unsaturated monomer and a hydrophobic co-stabilizer. Without wishing to be bound by any mechanism, it is believed that a greater portion (preferably substantially all) of the amphiphilic stabilizing polymer is located at or near the interface between the dispersed and continuous phases. When the stabilizing polymer is in the deprotonated state, the solubility of the stabilizing polymer in the monomer is preferably less than about 2%, more preferably less than about 1% (based on the total amount of monomer, by weight) .

"Substantially stable" means that the microemulsion has a sufficiently long shelf life that the monomers dispersed within the emulsion are able to polymerize within the droplets and the phases have sufficient time to separate before the emulsion destabilizes. The microemulsions obtained by the method of the present invention generally have a shelf life of more than 24 hours, often more than several days.

In step (c) of the process of the invention, the monomers within the droplets are polymerized. The monomers are usually polymerized under free radical polymerization conditions, preferably in the presence of a free radical initiator. The polymerization initiator may be either a water-soluble or an oil-soluble compound. Suitable free radical initiators are well known in the art and include, for example, without limitation, organic peroxides such as benzoyl peroxide, lauroyl peroxide, 2,5-dimethyl 2,5-bis(2-ethylhexanoylperoxy)hexane and dicumyl peroxide; inorganic persulfates such as potassium, sodium and/or ammonium persulfates; and azo-based initiators , such as azobisisobutyronitrile (AIBN) and azobis(1-cyclohexanecarbonitrile); and/or a pair of redox agents, such as Fe ²⁺ /H ₂ O ₂ , ROH/Ce ⁴⁺ ( wherein R is an organic group, such as C _1-6 alkyl or C _5-8 aryl) and/or K ₂ S ₂ O ₈ /Fe ²⁺ (any of them with for example ascorbic acid and/or one or more Bisulfite pairing) those counterparts. Optional polymerization initiators which may also be added to the first and/or second premix formed in step (a) may also be selected from those listed herein.

The radical initiator can be added after, before and/or during step (b). When the optional first and second premixtures are prepared in step (a) and the solubility of the initiator in the second premixture is higher than in the first premixture, the initiator is preferably added to the second premixture in the mixture. However, if the initiator is more soluble in the first premix, it is preferably added at the end of step (a) (after the mixture has been formed) or more preferably into the microemulsion obtained at the end of step (b).

During the polymerization step (c) of the present invention, in order to keep the stabilizing polymer in an amphiphilic state, it may be necessary to add other pH-adjusting compounds as described for step (a), especially those whose pH drops during the polymerization. case. The drop in pH may be caused by the decomposition of the persulfate initiator (eg ammonium persulfate) and/or as any pH adjusting compound already present in the mixture (eg when ammonia is used) evaporates. The pH adjusting compound added in step (c) may be the same or different from any adjusting compound added in step (a).

The polymerization of step (c) can be carried out at a wide temperature range, depending on the choice of initiator, preferably from about 20 to about 90°C, more preferably from about 25 to about 80°C, eg about 70°C.

The polymerization of step (c) is generally carried out over a period of time ranging from about 10 minutes to about 24 hours, more usually from about 2 to about 10 hours, most usually from about 4 to about 6 hours.

The present invention also relates to aqueous polymer dispersions (referred to herein as polymer emulsions, microemulsions and/or polymer latexes) obtained and/or obtainable by the process of the invention described herein, and to Bulk collectible (dry) polymer.

Broadly in yet another aspect of the present invention, there is provided an aqueous polymer dispersion comprising a matrix of polymer particles formed from at least one α,β-ethylenically unsaturated monomer, the particles having a diameter of about 10 to about 1000 nm and uniformly dispersed therein by the polymer matrix is: (i) at least one of a number average molecular weight (Mn) of about 800 to about 100,000 Daltons and an acid value of about 50 to about 400 mgKOH/g an amphiphilic stabilizing polymer; and (ii) optionally at least one hydrophobic co-stabilizer.

Optionally, the polymer dispersion of the present invention is subject to at least one of the following conditions:

(w) the dispersion contains less than 0.1% of the total amount of any nonionic surface active compound;

(x) the dispersion has a solids content of at least 22% by weight;

(y) the optional hydrophobic co-stabilizer is substantially colorless; and/or

(z) Amphiphilic Stabilization Any acid groups on the polymer are neutralized with at least one strong base, optionally selected from alkali metal hydroxides and ammonia.

The aqueous polymer dispersions of the present invention may comprise polymer particles having an average particle size approximately the same as the average size of the droplets in the microemulsion from which the polymer particles are formed.

Preferred polymer latexes of the present invention have an average diameter of from about 10 to about 900 nm, more preferably from about 50 to about 500 nm, most preferably from about 50 to about 400 nm, for example from about 80 to about 350 nm.

Preferred aqueous polymer dispersions of the present invention have a solids content of from about 25% to about 60%, more preferably from about 28% to about 50%, by weight of the dispersion.

The polymer latexes of the present invention may have good stability, preferably at least 6 months; and have similar uses to known latexes. Preferred uses include the preparation of decorative and protective coatings, films, pressure sensitive adhesives, inks, glues, stains, varnishes, structural adhesives, and the like.

Coatings and films obtained from the latexes of the invention have improved water resistance and reduced water absorption. They may also exhibit less blush when exposed to water, improved gloss, better blocking resistance and/or high film hardness.

Other aspects of the invention are given in the claims.

The following non-limiting examples are described to illustrate the invention.

Example 1:

1(a)(i) Preparation of the first premix (aqueous solution of the amphiphilic stabilizing polymer):

Copolymer (60 g of styrene, α-methylstyrene and acrylic acid copolymer, Mn = 6500 and acid number 193 to 215 mg KOH/g, commercially available from Rohm & Haas under the trademark Morez ^™ 101) was added to 17.9 g ammonia (25% w/w) and 125 g of demineralized water while stirring. The resulting mixture was then heated to 70°C and stirred until the copolymer was completely dissolved. The resulting solution had a solids content of 29.7% (w/w).

1(a)(ii) Preparation of second premix (co-stabilizer & organic solution of monomer)

A hydrophobic co-stabilizer (0.29 g hexadecane) was dissolved in α,β-ethylenically unsaturated monomer (14.4 g styrene).

1(a) forms a mixture:

The first premix (2.28g) from Step 1(a)(i) was diluted with 57.6g demineralized water. The second premix of step 1(a)(ii) was added directly to the diluted first premix while stirring the resulting mixture at 1000 rpm for 10 minutes using a magnetic stirring bar.

1(b) Preparation of Microemulsion:

The mixture of the preceding step 1(a) was subjected to high stress for up to 10 minutes. The resulting microemulsion had a droplet size of approximately 191 nm.

1(c) polymerize the monomer:

Potassium persulfate (0.07 g) was dissolved in the microemulsion from step 1(b). The resulting mixture was then transferred to a sealed glass vial and placed in a water bath (70°C) for 6 hours. The obtained polymer dispersion had a particle size of 176 nm and 1.4% of the polymer was agglomerated.

Example 2

Example 1 was repeated, except that the mixture was treated with ultrasound for 5 minutes in the same manner as in the preparation of the microemulsion in step (b). The microemulsion formed had a droplet size of approximately 416 nm. The resulting polymer dispersion had a particle size of 124 nm and 7.6% of the polymer was agglomerated.

Example 3

3(a)(i) Preparation of the first premix (aqueous solution of the amphiphilic stabilizing polymer):

Copolymer (80 g of styrene-maleic anhydride copolymer, acid value 165 to 205 mgKOH/g, commercially available from Atofina under the tradename SMA1440) was added to a mixture of 21 g ammonia (25% w/w) and 400 g demineralized water , while stirring. The resulting mixture was then heated to 70°C and stirred until the SMA resin was highly dissolved, then 100 g of additional demineralized water was added. The aqueous solution was decanted to separate from the undissolved SMA resin, resulting in a solution with a solids content of 8.3% (w/w).

3(a)(ii) Preparation of second premix (organic solution of co-stabilizer & monomer)

The hydrophobic co-stabilizer (5.72 g hexadecane) and the α,β-ethylenically unsaturated monomer (200.2 g methyl methacrylate and 85.5 g butyl acrylate) were gently stirred together. Then 2.86 g of 1,1'-azobis(1-cyclohexanecarbonitrile) (commercially available from Wako under the trade name V40) was dissolved in the mixture.

3(a) to form a mixture:

Demineralized water (636 g) and nonionic surfactant (0.44 g of a mixture of ethoxylated linear fatty alcohols, commercially available from Cognis under the trade mark Disponil ^™ A3065) were mixed together in a 1.2 liter measuring beaker. A first premix of SMA (68.9 g, prepared similarly to the method described in Step 3(a)(i)) was added to the water and surfactant mixture. The second premix of step 3(a)(ii) was added directly and slowly while stirring the resulting mixture continuously for 30 minutes.

3(b) Preparation of Microemulsion:

The mixture obtained in the preceding step 3(a) was added to a beaker in a water bath. The bulk mixture was stirred using a magnetic stirrer. While cooling the mixture in a water bath, the mixture was subjected to high stress for 10 minutes using ultrasonic waves (generated by a 400 W ultrasonic probe, commercially available under the trade name Dr. Hielscher UP40OS, with an amplitude setting of 60% and a duty cycle of 0.9). Thus a microemulsion is obtained.

3(c) polymerize the monomer

The microemulsion obtained from step 3(c) was transferred to a 1 L double-jacketed glass reactor connected to a water bath and equipped with a mechanical anchor stirrer. The mixture was heated to 70°C and this temperature was maintained for 4 hours. The mixture was then cooled and filtered. The resulting polymer dispersion contained 28.5% solids and had an average particle size of 195 nm.

Example 4

4(a)(i) Preparation of the first premix (aqueous solution of the amphiphilic stabilizing polymer):

Copolymer (60 g of styrene, α-methylstyrene and acrylic acid copolymer, Mn = 1200 and acid number 235 mgKOH/g, commercially available from Rohm & Haas under the trade mark Morez ^™ 300) was added to 20.5 g of ammonia (25% w /w) and 125g of demineralized water while stirring. The resulting mixture was then heated to 70°C and stirred until the copolymer was completely dissolved. The resulting solution had a solids content of 29.3% (w/w).

Step 4(a)(ii).4(a).4(b)&4(c). Preparation of Second Premix, Mixture & Microemulsion, & Polymerization

Polymer dispersions were prepared as described in Example 1 Steps 1(a)(ii), 1(a), 1(b) & 1(c), except that the preceding Step 4(a)(i) The first premix of substituted for the first premix of step 1(a)(i) of Example 1. The average droplet size of the microemulsion obtained in step 4(b) was about 177 nm. The obtained polymer dispersion had a particle size of 163 nm and 1.3% of the polymer was agglomerated.

Example 5

5(a)(i) Preparation of the first premix (aqueous solution of amphiphilic stabilizing polymer)

The first premix was prepared as described in Example 1(a)(i).

5(a)(ii) Preparation of second premix (organic solution of co-stabilizer & monomer)

Hydrophobic co-stabilizers (0.59 g hexadecane and 0.59 g 2,5-dimethyl 2,5-bis(2-ethylhexanoylperoxy)hexane, available from Atofina under the trademark Luperox ^™ 256 ) was dissolved in α,β-ethylenically unsaturated monomer (29.6 g butyl acrylate) to form a second premix.

5(a) to form a mixture:

The first premix (1.97 g, obtained from Example 1(a)(i)) was mixed with 44.2 g of water and the second premix of step 5'(a)(ii) was added while stirring the mixture with a magnetic stir bar. Mixture for 10 minutes.

5(b) Preparation of Microemulsion:

The mixture of the preceding step 5 (a) was added to a beaker in an ice bath and the mixture was cooled in an ice bath while ultrasonic waves (generated by an ultrasonic device, purchased under the trade name BransonSonifier 450, output controlled at 8, Duty cycle 80%) treatment subjected the mixture to high stress for 5 minutes, resulting in a microemulsion with an average droplet size of approximately 165 nm.

5(c) polymerize the monomer

Transfer the microemulsion from step 5(c) to a sealed glass bottle and let it submerge in a water bath at 70°C for 6 hours. The resulting polymer dispersion had an average particle size of 310 nm, a solids content of 39.7% (w/w) and the polymer was found to agglomerate only slightly.

Example 6

6(a)(i) Preparation of the first premix (aqueous solution of the amphiphilic stabilizing polymer):

The first premix was prepared as described in Example 1(a)(i)

6(a)(ii) Preparation of second premix (organic solution of co-stabilizer & monomer)

A hydrophobic co-stabilizer (0.31 g hexadecane) was dissolved in the α,β-ethylenically unsaturated monomer (14.4 g butyl acrylate) to form a second premix.

6(a) Prepare the mixture:

The first premix (2.28 g, obtained from Example 1(a)(i)) was mixed with 57.6 g of demineralized water. The second premix of step 6(a)(ii) was then added to the diluted first premix over 10 minutes while stirring the mixture at 1000 rpm with a magnetic stir bar.

6(b) Preparation of Microemulsion

Continue to stir the mixture obtained in the aforementioned step 6 (a) to mix the body, and simultaneously use ultrasonic waves (generated by a 400w ultrasonic probe, purchased under the trade name Dr.Hielscher UP40OS, the amplitude is set to 90%, and the duty cycle is 0.8) to process The mixture was subjected to high stress for 10 minutes. microemulsion

6(c) polymerize the monomer

Ammonium persulfate (0.07 g) was dissolved in the microemulsion from step 6(b). The mixture was then transferred to a 100 ml three neck glass reactor equipped with a reflux condenser and an oil bath. The mixture was heated to 70°C and maintained at this temperature for 6 hours. The resulting polymer dispersion had an average particle size of 134 nm and only 0.5% of the polymer was agglomerated.

Example 7

7(a)(i) Preparation of the first premix (aqueous solution of the amphiphilic stabilizing polymer):

The first premix was prepared as described in Example 1(a)(i).

7(a)(ii) Preparation of second premix (organic solution of co-stabilizer & monomer)

Hydrophobic co-stabilizers (0.72 g hexadecane and 0.72 g 2,5-dimethyl 2,5-bis(2-ethylhexanoylperoxy)hexyl available from Atofina under the trademark Luperox ^™ 256 alkane) in α,β-ethylenically unsaturated monomer (36.1 g methyl methacrylate) to form a second premix.

7(a) Preparation of mixture

A first premix (2.4 g, obtained from Example 1(a)(i)) was mixed with 35.1 g of demineralized water. The second premix of step 7(a)(ii) was then added to the diluted first premix while stirring the mixture for 10 minutes.

7(b) Preparation of Microemulsion:

The mixture from the previous step 7(a) was added to a beaker in an ice bath and the mixture was allowed to cool in the ice bath to keep the temperature low enough to prevent polymerization while passing ultrasonic waves (produced by an ultrasonic device under the trade name Branson Sonifier 450, output control set to 8, duty cycle to 80%) the mixture was subjected to high stress for 10 minutes to obtain a microemulsion with an average droplet size of approximately 128 nm.

7(c) polymerized monomer

The microemulsion from step 7(b) was transferred to a glass vial, which was immersed in a water bath at 70°C and polymerized continuously at this temperature for 6 hours. The resulting polymer dispersion had an average particle size of 245 nm and 49.8% solids. The amount of coagulated polymer was negligible.

Example 8

8(a)(i) Preparation of the first premix (aqueous solution of the amphiphilic stabilizing polymer):

The first premix was prepared as described in Example 3(a)(i).

8(a)(ii) Preparation of second premix (co-stabilizer & organic solution of monomer)

A hydrophobic co-stabilizer (5.7 g of a mixture of C _18-22 acrylates, commercially available from Atofina under the trademark Norsocryl ^™ A-18-22) was dissolved in the α,β-ethylenically unsaturated monomer (96 g of methyl methyl acrylate and 41 g butyl acrylate) to form a second premix.

8(a) Preparation of mixture

The first premix (68.9 g, obtained from Example 3(a)(i)) and 10 g of a 5% aqueous sodium hydroxide solution were added to 275 g of demineralized water. The second premix of step 8(a)(ii) was then added directly to the diluted first premix while stirring the mixture for 10 minutes.

8(b) Preparation of Microemulsion

Utilize a magnetic stirrer to continue to stir the mixture of the aforementioned step 8 (a) to mix the body, and simultaneously pass ultrasonic waves (produced by a 400w ultrasonic probe, purchased with trade name Dr.Hielscher UP40OS, the amplitude is set to 60%, and the duty cycle is 0.9) Treatment The mixture is subjected to high stress for 10 minutes. microemulsion

8(c) polymerize the monomer

The step 8(b) microemulsion was transferred to a 1 liter double jacketed glass reactor connected to a water bath and equipped with a mechanical anchor stirrer. Ammonium persulfate (0.8 g) was added to the microemulsion and the mixture was heated to 70°C and held at this temperature for 6 hours before cooling and filtering the mixture. The resulting polymer dispersion contained 28.4% solids with an average particle size of 123 nm. Samples taken from the mixture during polymerization after 2 and 4 hours were measured to have average particle sizes of 114 and 119 nm, respectively.

Example 9

9(a)(i) Preparation of the first premix (aqueous solution of the amphiphilic stabilizing polymer):

The first premix was prepared as described in Example 3(a)(i).

9(a)(ii) Preparation of second premix (organic solution of co-stabilizer & monomer)

A hydrophobic co-stabilizer (20 g mixture of C _18-22 acrylates, commercially available from Atofina under the trademark Norsocryl ^™ A-18-22) and a polymerization initiator (3.8 g dilauroyl peroxide, available from Akzo Nobel as (available under the trademark Laurox S ^™ ) was dissolved in α,β-ethylenically unsaturated monomer (a mixture of 250 g methyl methacrylate and 250 g butyl acrylate) to form a second premix.

9(a) Prepare the mixture:

The first premix (241 g, obtained from Example 3(a)(i)) was added to 1031 g of demineralized water with 20 g of 5% aqueous sodium hydroxide solution, and the second premix of step 9(a)(ii) Add directly to the diluted first premix while stirring the resulting mixture for 10 minutes.

9(b) Preparation of Microemulsion:

The crude emulsion from step 9(a) above was subjected to high shear using a high shear mixer (commercially available from Microfluidics ^™ under the trade designation M-110Y Microfluidizer® processor and equipped with an F20Y interaction chamber and a H30Z auxiliary processing module). effect. The emulsion was passed through the shearing device three times and the product outlet cooled to avoid polymerization. A microemulsion is obtained.

9(c) polymerize the monomer

The microemulsion obtained from step 9(b) was transferred to a 2.5-liter double-jacketed glass reactor connected to a water bath and equipped with a mechanical anchor stirrer. The microemulsion was heated to 70°C and maintained at this temperature for 6 hours, then the mixture was cooled and filtered. The resulting polymer dispersion contained 28.0% solids and had an average particle size of 116 nm. The amount of coagulated polymer was negligible.

Comparative example A (comparative embodiment):

Example 6 was repeated without subjecting the mixture formed in step 6(a) to high stress by sonication (ie step 6(b) was omitted). The resulting polymer dispersion had an average particle size of 930 nm, with 3.3% of the polymer agglomerated. The dispersion was unstable and partial phase separation was observed after 24 hours.

Claims (21)

1. prepare the method for aqueous polymer dispersion by microemulsion polymerization, this method comprises the following steps (a) forming a mixture comprising: (i) water; (ii) at least one amphiphilic stabilizing polymer having a number average molecular weight (Mn) of about 800 to about 100,000 Daltons and an acid value of about 50 to about 400 mg KOH/g; (iii) at least one hydrophobic co-stabilizer; and (iv) at least one α,β-ethylenically unsaturated monomer; wherein the mixture comprises no more than about 2% by weight, relative to the total amount of any other ingredients, of a monomer that acts as a surfactant in the mixture; (b) applying high stress to the mixture of step (a) to form a substantially stable microemulsion comprising a continuous aqueous phase and dispersed therein stable droplets having an average diameter of about 10 to about 1000 nm, the liquid Droplets contain hydrophobic co-stabilizers and monomers; (c) Monomers polymerized inside the droplet. 2. The method according to the preceding claim, wherein in step (a) the mixture is formed by mixing a first (aqueous) premix with a second (organic) premix, wherein the first premix comprises amphiphilic stabilized Using polymer and water, the second premix contains hydrophobic co-stabilizers and α,β-ethylenically unsaturated monomers. 3. The method according to claim 2, wherein a polymerization initiator is introduced (optionally dissolved) in the second premixture. 4. A method according to any preceding claim, wherein the amphiphilic stabilizing polymer is a polymer obtained from a combination of a hydrophobic monomer and a hydrophilic monomer comprising an acid function or a function capable of forming the acid function . 5. A method according to any preceding claim, wherein the amphiphilic stabilizing polymer comprises a copolymer formed from styrene and maleic anhydride and/or from styrene, alpha-methylstyrene and acrylic acid. 6. A method according to any preceding claim, wherein the solubility of the amphiphilic stabilizing polymer in the aqueous phase, measured at 25°C, is at least about 1 x ^10-2 g/l. 7. A method according to any preceding claim, wherein the amphiphilic stabilizing polymer is used in an amount of from about 0.5% to about 15% by weight relative to the total amount of α,β-ethylenically unsaturated monomers. 8. A method according to any preceding claim, wherein the solubility of the hydrophobic co-stabilizer in water, measured at 25°C, is less than about 5 x 10 ^-5 g/l. 9. A method according to any preceding claim, wherein the hydrophobic co-stabilizer is selected from the group consisting of C _12-14 alkanes, C _12-14 alcohols, C _18-22 acrylates and mixtures thereof. 10. A method according to any preceding claim, wherein the hydrophobic co-stabilizer is present in an amount of from about 0.05% to about 40% by weight, based on the total amount of the mixture prepared in step (a). 11. A method according to any preceding claim, wherein the solubility of the α,β-ethylenically unsaturated monomer in water measured at 25°C is less than about 15%. 12. A process according to any preceding claim, wherein the α,β-ethylenically unsaturated monomers are selected from the group consisting of styrene, acrylates, methacrylates, vinyl halides and vinylidene halides, dienes, vinyl esters and its mixture. 13. The method according to any preceding claim, wherein one or more monomers having a water solubility measured at 25°C higher than about 15% are added to the mixture of step (a) in an amount lower than the total monomer About 6% by weight of body mass. 14. A method according to any preceding claim, wherein one or more pH adjusting components are added to the mixture formed in step (a). 15. A method according to any preceding claim, wherein step (b) produces a microemulsion comprising stabilized droplets having an average particle size of from about 50 nm to about 500 nm. 16. A method according to any preceding claim, wherein the high stress in step (b) is applied by means of means producing localized high shear, optionally in combination with moderate bulk mixing. 17. A method according to any preceding claim, wherein the monomers within the droplets are polymerized in the presence of a free radical initiator. 18. A stable aqueous polymer dispersion obtained and/or obtainable directly or indirectly from a process as claimed in any preceding claim. 19. A stable aqueous polymer dispersion comprising a matrix of polymer particles formed from at least one α,β-ethylenically unsaturated monomer, the particles having an average particle diameter of from about 10 to about 1000 nm, and being polymerized The material matrix is uniformly dispersed therein: (i) at least one amphiphilic stabilizing polymer having a number average molecular weight (Mn) of about 800 to about 100,000 Daltons and an acid value of about 50 to about 400 mgKOH/g and (ii) optionally at least one hydrophobic co-stabilizer. 20. Use of a polymer dispersion according to any one of claims 18 or 19 for the preparation of coatings, films, adhesives and/or ink compositions. 21. Coating, film, adhesive and/or ink composition obtained and/or obtainable using a polymer dispersion as claimed in any one of claims 18 or 19.